Photodynamic therapy (PDT) is a promising cancer treatment. PDT uses the affinity of photo-sensitizers such as hematoporphyrin derivative (HPD) and other compounds to be selectively retained in malignant tumors in malignant tumors. When tumors, pre-treated with the photosensitizer, are irradiated with visible light, a photochemical reaction occurs and tumor cells are destroyed. Oxygen molecules in their metastable single delta state O2 (1delta) are believed to be the species that destroys cancerous cells during PDT. A real-time optical diagnostic for singlet oxygen in-vivo would be a valuable dosimeter during PDT treatment. Physical Sciences Inc. proposes to develop and test an optical monitor for singlet oxygen that provides 10/3 sensitivity improvement over current detection techniques. In this Phase I we propose in-vitro tests with several photosensitizers in numerous solvents, including aqueous solutions containing strong quenchers of singlet oxygen. The successful demonstration of the diagnostic could lead to numerous applications. For example, one could study the photo-induced HPD process in much more detail. New porphyrin compounds could be screened for O2 (1delta) production efficiency. Finally a real time O2 (1delta) monitor during phototherapy could be an invaluable tool for improving the efficiency of cancer cell destruction. PROPOSED COMMERCIAL APPLICATIONS: There are several commercial applications. First, a real-time diagnostic tool for O2 (1delta) production could be produced using fiber optic technology. A surgeon could use this tool to measure and maximize the O2 (1delta) produced during treatments. Secondly, a tool could be developed to test new photoactive compounds for their ability to produce O2(1delta). One could also use the tool as a quality control device in mass production of these HPD-related compounds. Finally, it could also be a valuable research tool for developing a better understanding of the mechanisms and kinetics in PDT.